Manufacture of zinc sulphide pigment



Nov. 12, 1935. A J. MYHREN Er AL 2,020,902

MANUFACTURE OF ZINC SULPHIDE PIGMENT Filled neg. 15, 1955 Y INVENTORS ARA/E j', /l//V//E/V BYRON. MARQUIS BY. i l

ATTORNEYS .30 of crudepreci Patented Nsv'; 12, 1935 i VUN-ITED STATES APA moslims Arne J.

Pgsasign NevYo'l-k,

licking cslcinstion: (7) wetgrinding, l(8) and disintegration. sment is obtained after ng operations.

water,

Vzinc sulphide pi usion oihthese 4zine sulphide pigment with higher tin strength than rapid settling slm-ries, other things equal. present inyention contemplates A sample oi' 500 cubic centiieters of the slurry pitate is taken befo rved for 1 slurry is obse in a graduated crude .precipitate ,that 60. cubic centimeters ing methods. .Thus a settles y'so as to yield 30to oi clear,4

inches iilled to indepth mate diamete'oi' 1% A (a. supernatant .f liquor 'a pigment that is deficient in The slow settling crude preciporsto'l'h New'Jency' BncCompmy N. ln'lrponuenolhlcwluny Appliostion December l5, 1933,

re skins. This l i precipitation .may

.4 inches) will yield after'` TENT: osi-*ics Myhren and Byron v No, mm w1., ,ssiw litajm yield on drying a rlpidsettlingreude prec hud crude cake. 'me ipitates yield on drying trema; slow seta crude precipitate can be ob Inthe process ot the invention the .zinc

.phate solution and hydrogen sulphide gas between the hydrogen sulphide and the zinc sulphate 'is facilitated and accelerated by the $0 intimacy oi' contct sopbtained. The limiting thisreaction is the rate keeping the zinc i so mto able apparatus for the practice-of the invention.

Fig. 2 is a section on the line 2-2 of Fig. 1, showing in detail the construction of the Venturi tube eductor 6, and likewise of the eductors 6',-

5", 1, 1' and 1" inFig. Al.

'I'he apparatus illustrated in the drawing com prises three tanks 5,152 5" (arrang'ed series),

of circular cross-section and with conical-bottoms, each tank being provided with two Venturi tube eductors 6 and 1, 6 and 1 and GVand 1", respectively. The series of tanks is provided with a'gas inlet pipe 8" (entering the top portion of tank 5") and a gasoutlet pipe 3(dis charging from tank 5). A gas pipe 8' connects the top portions of tank 5" and 5 and a gas pipe 8 connects the top portions of tanks 5 and 5. The -system of pipes 8", 8', 8 and 9 connects the tanks in series at points above the normal level (a) of liquid or slurry' therein in such fashion Athat gas can flow freely through the series of tanks. The gas outlet pipe 9 dips below the 'liquidlevel (b) in a water seal I0. The gas-space abovel ce the liquid-level (b) in the water seal Ill is con'- nected by a pipe with the suction side of a fan. I2. The pressure side of the` fan |2 is connected by a pipe I3 with a screen-box I 4, which contains metal screens (preferably made of a metal of high heat conductivity such as copper) set across the path of the gases therethrough. The screen box I4 is connected by a pipe I5 to agas burner I6, provided with a stack I'l.

The metal screens in the box Il prevent backfiring of the il'ame in the gas burner I6. The water seal I0 is yofA utility not only asa further safe-guard against back-ring, but also as a ,means of regulating the effective suction of the ian 2. The eiective suction of the fan I2 on 4m the outlet pipe 9 may be increased by lowering vthewater--level (b) in the water seal I0, and

decreased by raising the water level. Moreover, the water seal 'I0 prevents the entrance of air into the tank 5 when the fan I2 is shut down, g or example for the purpose of attaching a spare an. 'Ihe tanks 5, 5- and 5" are v provided with pumps for liquid and/or slurry transport, and pipe lines for liquid or slurryare appropriately 5@ connected with the pumps, tanks and"Venturi tube ,eductors in such fashion that liquid and-l or slurry-can be transported through the series of tanks and vlikewise partly recirculated in the individual tanks, while being brought into intimate contact with -gas traversing the series of tanks in Vgeneral countercurrent with the liquidV and/or slurry. Each oi the' six Venturi tube eductors (3, 1, 6', 1', 6" and1) is arranged to recirculate gas through the tank with which itis operatively associated,-whi1e intimately mixing the gas with the' liquid and/or slurry. The Venturi tube eductor 6 introduces liquid into the system by discharging it into tank 5. The Venturi tube eductors 1, 1' and 1" serve rvto recir- M culate liquid or slurry through the tanks with which they are connected (through tanks 5, 5' and 5", respectively). The Venturi tube eductors 3'A and 6" serve to convey liquidlor slurry m, from one tank into the next' tank in' the series.

' Thus, Venturi tube eductor 6'4 serves to convey liquid or slurry (withdrawn from tank 5) into tank 5'; and Venturi'tube eductor 6" serves tol (withdrawn from tank convey liquid or slurry The apparatus shown in Fig. lvwill now bel described in greater detail:

A pump 20 is connected on its suctionv side to a source of liquid (not shown). On its pressure side,` the pump 2|! is connected with aV pipe 2|, 5 part of which consists of the rubber hose segment 22, provided with-a pinch valve 23. The pipe ,2| leads to' the Venturi tube eductor 6. Between the pinch valve 23 and the eductor 6, the pipe 2| is provided with a pressure gauge 2l, for 10 indicating the rate of delivery of liquor to the Venturi tube eductor 6.

The structure of the Venturi tube eductor 6 will be more clearly understood by reference to Fig. 2. The pipe 2| connects with a duct 25, in l5' which is placed a spiral baillel 26. The duct 25 terminates in a discharge nozzle 21 in a gas chamber 28, connected by a pipe 23-to the upper portion of the tank 5 `(i; e., the portion of the tank 5 above the line of normal slurry o r liquid 20 level a therein) .v The nozzle 21' is placed concentrically with a Venturi tube 30 communicating with the gas-chamber 28,at a point opposite' the nozzle 21.

Referring again to Fig. 1, the suction side of 2,5A

a pump 3| is connected by a pipe 32 to the discharge orice at the tip of the conical bottom of tank 5. The -pressure side of pump V3| is connected to a pipe 33, dividing at its upper end into a branch pipe 34 leading back 30;. into the tank 5 through the Venturi tube eductor 1, and into branch pipe 2|', leading into the Venturi tube eductor 6'. The branch pipe 3l is provided with the rubber hose segment 35, equipped with the pinch valve 36, and is also pro- :25; vided with the pressure gauge; 31,` between the pinch valve 36 and the Venturi tube eductor 1. The branch pipe 2| is likewise provided with a rubber hose-section 22' equipped with a pinch valve 2 3', and provided with a pressure gauge 24' 4,0'r between the pinch valve 23' and the Venturi tube -eductor 6. It will be readily understood that the relative amounts of liquid (or slurry) enterving the branch pipes 34 and 2|', respectively, can

explained, by appropriate adjustment of the pinch valves 23' and 36', respectively; and that the relative -amounts of liquid or slurry iiowing through the pipes 2|' and 34 can be determined `fat any time by comparing the reading 50, of the gauges 2l'v and 31. I r The structure of the Venturi tube eductors 6", 1, 1 etc. is the, sameas that'of Venturi tube eductor 6 hereinbefore described. Pipe I9, 9'

and I3" Vconnect the upper portion of the tanksgn;

5, 5' and 5" with the gas chamber of .the Venturi tube eductors 1, 1 and 1^', respectively., 1

The structure and arrangement of the pump 3|', pipes 32'.. and 33', branch pipe 34' with the rubber 'hose segment'35', pinch valve 36' and s gauge 31', branch pipe 2|" with the rubber segment 22",r pinch valve 23" and gangen", and the Venturi tube eductors 1' and lii", are the same withrespect to tanks 5 and 5" as the Astructure-and arrangementof the correspond- 55.

ingly identied elements described with respec totanksandi'.. .i l The pump 3|" is connected on its'lsuction yside tothe pi'pe 32" communicating with the discharge orifice in theconical bottom of the 5". Thepressure side of the pump 3|" is'connected to the pipe 33", which divides .into the branch pipe A34" (connecting with the VenturiV tube eductor 1") Aand branca pipe 38,-which i serves as an outlet for the discharge of Aliquider 751,

55 -From ther pipe 2|, the

. amm i a' slurry from the The branch pipe vWis provided with the hose segment ll", having :he pinch valve It", and with the Venturi tube. eductor 1i" appropriate adjustment o! the valves 4land and that the amount of liquid or slurry entering the Venturi tube eductor can be dcter' mined at any time by reading the gauge il",

Hydrogen sulphide is introduced into the series of tanks through the inlet l", and circulated fn zo .succession through tunic s", pipe s', tank s', pipe I, tank I, outlet piped and water-seal I l by 30' water-seal III prevents reason, as forexample for the purpose of attaching a spare fan to the gas outlet line s.

e The ian I 2 forces the gas through the line Il,

the screen burner Il. The products of combustion (e. g.

sulphur dioxide) are removed from the burner VBack-tiring of yllame from the burner I6 into the system is guarded against 40 'by metal screens (made of a metal of high heat conductivity, e. g. copper) placed in the path of the gases in screen-box i4.- The water-seal Il is a further safe guard against back-firing.

ed zincsuiphate solution is introduced' (preferably continuously) into the system by pump Il, which delivers solution to the Venturi tube eductor I through the pipe 2|. The amount of solution 't ed in the pipe line 2 I. at a point between the Venturi tube eductor I and the pinch valve 23.

solution Aenters the -duct 2l o! the Venturi tube eductor 8. A swirling motion is imparted to the solution flowing through the duct 25 by the' spiral baille 2l.` The swirling stream of solutionthen passes through go the nozzle 21 inthe form of a conical expanding jetinto the gas chamber Il. Theiet traverses the gas-chamber 28 and enters the Venturi tube oi' the jet of solution is suiliciently increased byV pressuregauge the solution in the form oi' thin films The discharge pipe vIl is provided with a vuiuc sulphide, uiuc cmpiiuic and suipnunc regulated by box I4 and the line I5' t'o the gasA desirable uniform and rted by the pump 2l through tion ofthe `gils withfthc solution. into the tank I, 111e gas isbrought into intimate contact withy and small droplets in the .Venturi tubellso that the reacbetween hydrogen sulphide and sine sul- 5 phate is initiated, with formation of a slurry of volume of gas greatly in excess of the volume 10 of solution: for example. the volumeotliydrogen sulphide gas 4carried the Venturi tube eductor by'the solution may be from 25 to so same manner as theV Venturi tube eductor i. The' slurry entering the branch pipe 2| passes into the Venturi tube eductor I', which functions in the same manner as Venturi tube eductor l, with the slurry with It will be understood that in order'to secure a constant ilow of slurry through the apparatus. the Venturi tube eductor 45 l' hust transfer to the tank l 'an amount ci slurry corresponding to that entering the tank I through the `Venturi tubeeductor I5 The rate of discharge oi' Venturi tube eductor I' may be suitably controlled with'this-obiect in view by ap- 50 propriate.adiltment or the pinch valves It and 23'. Y

It will also be understood that the-capacityof the pump 3| must in consequence be adequate to pump all the slurry supplied to tank I by pump 55 ,2l plus the amount of slurry returned to, tankA i by the Venturi. tube eductor 1.

` The slurry charged into tank 5' by the Venturi tube eductor 6 is recircuiated in tank 5' through the Venturi tube ,eductor 1' and transported to iii)v tank 5f'. through the Venturi tube eductor 6" in amanner similar to that .lust described.

Slurry is withdrawn from tank I" by the pump 3l'.' through the' line 32", and pumped into the line I3", whence itis in part discharged from o5 the system through the line 38, and in part returned to tank 5" through the Venturi tube educ-1 tor 1". vThe ratio of the amount discharged throughthe'line 3l to that returned to tank 5" through Venturi tube eductor 1 is appropriately 7o controlled by proper adjustment of the lpinch valves 36" and I0. This adjustment isfacilitated by the 'fact that the readings of pressure 'gauge 3l" are an indication of the rate at which slurry is supplied to the Venturi tube eductor l".

f discharged from the sponds to the amount of slurry fedinto the sysof the conical bottom of '.3 In order to secure uniform and continuous ow of slurry through the system, it will in general be desirable to adjust the amount of slurry outlet 38 so that it corretem through the Ve turi tube eductor 6.

In the practice of the invention in tlie'apparatus illustrated in the drawing, it will generally be advantageous to -recirculate the slurry at a rate that is a multiple of the rate at which slurry is transferred fromtank to tank; for example, the ratio of volume of slurry recirculated to volume of slurry forwardedthrough the tanks may be 4:1, in case a ZnSOi solution containing 30 grams Zn per liter is used. In consequence, it is advantageous to construct the recirculating Venturi tube eductors 1, Ir 'and 1" larger than the transporting Venturi for example, the linear dimensions of 1, 1' and 1" may be twice those of 6, 6 and 6 In producing a zinc sulphide precipitate as hereinbefore described, the apparatus must of course be constructed of acid resistant material on account of the by the reaction -(ZnSOl-i-H2S=ZnS-}II 2 SO4.) Hard rubber, soft rubber, or steel lined with rubber are appropriate materials.

,In a practical example vof the invention carried out in the apparatus illustrated'in the drawing, each Aof the precipitation tanks is 5', 6" in diameter, has an overall height of 7', and the depth the tank is 5'. Each tank is adapted to contain from 150 to 200 gallons of zinc sulphate solution Aor slurry of pre- 1 cipitated zinc sulphide in zinc phuric acid solution, leaving ample room for an atmosphere of hydrogen sulphide gas above the liquid level. The-Venturi tube eductors are so operated'that the precipitator 6 is supplied with 2 0 gallons of zinc sulphate solution per minute and the transferring precipitators 6" and 6" discharge corresponding amounts of slurry. `The volume of feed entering the precipitators is controlled by adjusting the pinch valves in accordance with the pressure registered by the gauges in the downcomers leading to the precipitators.

The recireulating precipitators 1, 1 and 1" recirculate about 80 gallons of slurry per minute. Each Venturi tube eductor entrains from to 50 volumes (or more) of gas containing at least 50% of hydrogen sulphide gas for each volume of vliquor or' slurry. The gas introducedinto the apparatus (pipe 8") is substantially pure hydrogen sulphide (about 99.5% I-InS), and the exiting or spent gas (pipe 9) contains from 50i to 75%, hydrogensulphide'. The volume of exiting gas is of course very substantially smaller than the volume of gas introduced through pipe B" in consequence of the precipitating reaction, and since the only gases (other than hydrogen sulphide) entering the apparatus are relatively very small amounts of air, thev efficiency of hydrogen sulphide consumption in the apparatus Vis about 99.5-98.5%. The zinc sulphate solution treated contains about grams Zn per liter or about '15\ grams ZnSO4. per liter. In this operation, with three tanks in series, the slurry is'mixed with hydrogen sulphide gas in an eductor from ten to fifteen times before being discharged from the 70; apparatus, and there is substantially no .shortl circuiting of solution through the apparatus with.-

out adequate mixing with hydrogeiismphide gas. The slurry discharged through the outlet`38 `co n tains about 1.5 grams unprecipitated Zn per liter, and about 4.5% sulphuric acid. The elimination sulphate is increased to tube eductors 6, 6" and 6' formation of sulphuric acid sulphate and suli tained therefromv settles.

cipitation actually occurs is of ZnSO4 in the crude slurry as discharged from the precipitating system Ais thus 95% approximately. During the subsequent aging vtreatment lasting several hours in which the-crude zinc-'jsuiphide precipitate is maintainedlin contact fvith 5 the acid mother liquor, Atheelimimttlonifbffifinc i:

about"`98%'-' by?? rat'ln of the residual zinc sul hate with hydrogen -phide gas adsorbed by the zincv sulphide and gradually desorbed during the aging: i 1g The plant in question produces about five riet tons zinc sulphide pigment per day. After aging treatment, the precipitate isseparated from the mother liquor, dried, calcined Tand processed in a way similar to the finishing'l treatment of 15, Alitl'iopone.

Inaccordance with the present invention, the settling velocity of the crude z'inc sulphideprecipitate andthus the pigmentarypropertiesof the finished pigment' are controlled by modifying '20.

the following factors:

l. The concentration of the hydrogen sulphide gas in theeductor receiving fresh solution, that is, where the rst portion of the precipitate is formed. The greater drogen sulphide gas, the slower the' settling rate of the precipitate slurry. i This concentration is the concentration of the exiting gas in a countercurrentjsystem as shownin the drawing: Control of this concentration is obtainedl by regulat- 30 ing the eiliciency of the hydrogen sulphide ,gas absorption. For example, with a concentration of 99.5% HzS in the lgas entering the precipitating system and regulation of the gas absorption so as to give .a concentration' of 50% HzS in the 35 v centration of '75% HzS gas in the exiting gas (at 40 the eductor receiving-fresh solution), the efli-' ciency of the hydrogen sulphide gas absorption is about 98.5%. l Y

2. The temperature `of the zinc'sulphate liquor, which is the controlling factor of the temperature of the reaction. The higherthe temperature of the liquor the faster the crude precipitate ob- 3. The ratio between hydrogen sulphide-gas and zinc sulphatel solution in the Venturi precipitators. Since the reaction zone where the prefor the most part within the Venturi tube precipitators, the effective concentration of hydrogen sulphide gas is to a great extentv measured by the ratio tors. The higher the ratio of gas volume to liquor volume, the slower. the settling of the crude precipitate and the greater the tinting strength of the finished zinc sulphide pigment obtained therefrom, other factors being the same. With'zinc sulphate liquor containing 30 grams of `zincper liter and three precipitation tanks equipped with Venturi precipitators. in :the y manner hereinbefore described, an appropriate ratio of' gas' volume to liquor volume will for example. be between 25and 50 (or more) to 1.- 4. The ratio of' gallonage forwarded to gallonage recirculated. tion of recirculation, the faster the settling. g

`In general, any condition that tends to facilitate the precipitationreaction will tend at the same time, other factors being the same, to

produce a slow settling this concentration of hy- 25.

of gas volume to liquor volume in the Venturi precipita.-

The greater the propor-gl materiau` that will yield fr 030,902 y t 5f l a'finished zinc sulphide pigmentwitn nigh tintgen sulphide gas withrepeated contact of 'ing strength. resulting slurry with hydrogen sulphide gas in'a lIn controlling the operation by the applicaseries of tanks through which the slurry is passed tion of the principles herein described, it should with recirculation of slurry in each tank, the im- "5 be noted'that the control of the precipitation of provement which comprises providing a ratio of 5 the ilrst moiety of zinc present in the liquor is gas volume to liquor volume of between 25 and 50 the most important for determining the charto 1, and regulating with respect to each tank lthe acteristics of the crude precipitate. volume of slurry recirculated and the volume of Inpractlce, control of the settling rateisreadily slurry forwarded in the ratio of about 4 to- 1, l effected by regulating the gas concentration and whereby the settling rate of the crude zinc sul- 'i0 the ratio of recirculation to forwarding. In the phide precipitate is such that when500 cc. of case of zinc sulphate solutions containing 30 the slurry are left standingfor 10 minutes in a grains zinc Zn) per liter used in a system with cylindrical graduate of about 1% inches diamthree tanks, a ratio of 4 gallons recirculated liquor eter the crude zinc sulphide precipitate settles so l5 (slurry) to 1 gallon forwarded liquor (slurry) as to yield more than 30 cc. and less than 90 cc. 15

has been found appropriate to secure a desirable of clear supernatant liquor. `settling rate,` when using Venturi tube eductors 7. In the manufacture of zinc' sulphide pigwith a ratio of gas volume to liquor volume of ment by wet precipitation, in which a zinc salt -50 or more to 1. solution is brought into repeated contact in gen- 20 We claim: eral countercurrent flow with hydrogen sulphide 20' 1. In the manufacture of zinc lsulphide-piggas with recirculation of the esulting slurry, the ment by wet precipitation, in which a zinc 4sulimprovement which comprises regulating the eiliphate solution containing about grams of zinc ciency of hydrogen sulphide gas absorption so perliter is brought into contact with hydrogen that the concentration of hydrogen" sulphide in 25 sulphide gas, the improvement which comprises the gas rst contacting withfreshly introduced 25 providing a ratio of gas volume to liquor .volume zinc lsalt solution is at least 50%. ofbetween 25 and 50 to 1 for obtaining a crude 8.` In the manufacture of zinc sulphide pigzinc sulphide precipitate having a relatively slow ment by wet precipitation, in which a zinc salt settling rate. vsolution is brought into contact with hydrogen 30 2. In the manufacture of zinc sulphide plgsulphide gas with repeated contact of the result- 30 ment by wet precipitation. in which a zinc salt ing slurry with hydrogen sulphide gas in a series solution is brought intoscontact with hydrogen of4 closed tanks through which the slurry and gas sulphide gaswlth recirculation of the resulting passl in general countercurrently, the improveslurry, the improvement which comprises 'regument which comprises regulating the absorption lating the volume of slurry recirculated to the of hydrogen sulphide gassothat with an entering 35 '4 volumxe of slurry forwarded in the ratio of about gas containing at least 99% H28 the exiting gas 4 tof/1:

3. In the manufacture of zinc sulphide pig 9. In the manufacture of zinc sulphide piglnient -by wet precipitation, in which a zinc salt ment, the step which comprisesl treating zinc, 40 solution is brought into contact with hydrogen sulphate solution with hydrogen sulphide' gas by 40 sulphide gas with repeated contact of the resultrepeatedly reciroulating said solution in intimate of tanks through which the slurry is passed with at a concentration of at least Hrs by volume. recirculation 'of slurry in each tank, the improve- 10. In the manufacture of zinc sulphide pigvolume o1' slurry recirculated and the volume of ment which comprises mixing the solution and slurry forwarded in the ratio of about 4 to 1. .the hydrogen sulphide gas intimately and main- 50 4./-In the manufacture of zinc sulphide pigtaining. the concentration of Hrs in the residual 50 'ment by wet precipitation, in which a cold zinc gas in excess of 50%. y

sulphate solution containing about 30 grams of 11. In a method 0f making Zinc sulphide pigzinc per liter is brought into contact with hyment by the reaction between a zinc salt solution .drogen sulphide gas with recirculation of the reand hydrogen sulphide t0 1.01m a slurry 0f Crude sulting slurry, the improvement which comprises Zinc sulphide Particles 1,11 liquid. the mPrGVemeIit 55 regulating the vvolume of slurry recirculated to which comprises intimately mixing the zinc salt the volume or slurry forwarded in the ratio or solution with hydrogen sulphide gas maintained about 4 to l.

by wet precipitation, 1n which acold zinc sulphate .'30 t0 60 CCS; 0f Clear supernatant lqliid will 8P- 69 phide gas with repeated contact of the resulting 1%'iI1CheS diameter- Y slurry with hydrogen sulphide gas in a series of 12. In a method oi' making zinc sulphide pigtanks through Whichjthe slurry is passed with ment involving a reaction between a zinc salt so- 05 l recirculation of slurry in each tank, the improve- 111151011 and hydrgen sulphide with resultant forvolume to liquor volume of between 25 and 50 inliililidad slurry being recirculatedin Olltact to 1, and regulating with respect to each tank With hydrogen Sl11Dh1de..the improvement Which the volume of slurry recirculated and the volume comprises providing a ratio of gas to solution volj of slurry forwarded in the ration of about 4 to 1. ume ofbetween' 25 and50 to 1 and maintaining i 6. In the manufacture of zinc sulphide piga predetermined vratio between the amount of .ment by wet precipitation, in which o oom zinc slurry recirculated and the amount of slum adsulphate solution containing about 30 grams of winced. 1s, zinc per liter is brought into contact with hydro- 13. In a method oi.' makingzino sulphide pig- 75 ment involving an intimate contact between 'a zinc salt solution and hydrogen sulphide with the resultant formation of a slurry o! crude zinc sulphide particles in liquid, said slurry being in part recirculatedin contact with hydrogen sulphide gas, the improvement which comprises providing a ratio of gas to solution volume 'of between 25 and 50 to 1 and .maintaining a yprede-l termined concentration of the hydrogen sulphide gas in contact with the solution during the period of contact. Y

14. In a. method of making zinc sulphide pigkment by a reaction between a. zinc salt solution and hydrogen sulphide to form a slurry of crude zinc sulphide particles in liquid, the improvement which comprises intimately mixing the zinc salt solution with hydrogen sulphide gas maintained at a concentration in excess of V50% HzS until the resulting crude z nc sulphide slurry is such that more than 30 ccs. and less than 90 ccs. of clear supernatant liquid will appear when 500 ccs. of the slurry are left standing for 10 minutes in a cylindrical graduate of about l 1% inches diameter.

. ARNE J. MYHREN.

BYRON MARQUIS. 

